Methods of hardening and tanning of artificial fibers made of protein



Patented July 23, 1946 METHODS OF HARDENING AND TANNING OF ARTIFICIAL FIBERS MADE OF PROTEIN Rudolf Signer, Berne, Switzerland No Drawing. Application March '13, 1943, Serial No. 479,142. In Germany January 15, 1942 Claims. 1 This invention relates to methods of hardening and tanning artificial fibers made of protein substance.

,Artificial fibers made of protein substance, for

example of casein, have moderate physical properties such as for example a very small strength in wet condition, due to swelling in water.

Numerous methods for minimizing this drawback have already been proposed. Some of these are based on chemical effects such as hardening with formaline and tanning with aluminium,

chromium, or other metal salts. Further methods are of physical nature such as stretching and elongating methods which result in bringing about a higher order of conditioning of the particles of the fiber.

It has also already been proposed to combine chemical and physical effects by, for example, first stretching the spun fiber and hardening same in elongated condition with formaline or subjecting the fiber to an elongating process between a preliminary and a subsequent hardening with formaline.

It has now been discovered that extraordinarily great improvements on the strengths in wet and dry condition of the fiber can be obtained if a previous chemical effect is followed by a vigorous mechanical elongation and the elongated fiber is then subjected to a second but different chemical condensation.

The changing of the chemical condensing agent between the preliminary and the later elongation has a determinative influence as will be readily seen from the following comment. A casein fiber which has been preliminarily treated with formaldehyde has in wet condition an elasticity similar to rubber. If this fiber is elongated to double length and exhaustively hardened with formaline in elongated condition at room or elevated temperature the fiber shrinks on the cessation of the tension almost back into the length which it has had prior to the elongating.

Therefore, this treatment produces only a very small permanent elongation and a correspondingly small increase of the strength in wet and in dry condition. The same fiber, having been pre liminarily hardened with formaldehyde and elongated in wet state into double length and then tanned with chromium salt in elongated condition, shrinks on the cessation of the tension hardly any, while the strength in wet and in dry state is almost twice as great as before.

The three method steps, namely, the first chemical condensing, the mechanical elongation, and

the second chemical condensing can be carried out at different temperatures. Particularly, it is advisable to carry out the elongating at elevated temperature in connection with which the working can be considerably expedited and consequently also be rendered continual.

The succession of the chemical condensing operations can be chosen at will. The first operation may consist in a treatment with organic substances, such as aldehydes, chinone etc., the

second operation may consist in tanning with metal salts or vice versa.

Example 1 Fibers dry-spun from slightly alkaline caseinate are exhaustively hardened with formaldehyde vapor. For eliminating the alkali the fibers are dipped in diluted acid for a short time at room temperature. Thereupon the acid is washed out. The fibers are gathered into bundles in parallel relation and the latter are then slowly elongated in wet condition into double length at room temperature. The elongated bundles are submersed during four days, at a temperature of 20, in a bath containing g. of chrome alum and 10.6 g. of calcined soda per litre. The bundles are then washed and dried.

Example 2 A cord of long fibres having been hardened with formaldehyde is continuously unwound from a spool at a velocity of 1 in. per min. and simultaneously wound on a second spool at a velocity of 2 in. per min. The cord of long fibers is thus elongated into double length between the two spools. During the elongating the fibre is passed through a bath of water of 40 and subsequently introduced in a bath consisting in a chrome alum and calcined soda solution of the same composition as specified in Example 1. This bath moistens the fiber prior to being rolled up by the second spool, whereby the penetration of the chrome bath into the fiber is facilitated when the full spool is submersed in said bath.

The chrome solution is maintained at a temperature of 40. The elongation is effected by the two spools along a path of travel of about 6 m. The full spools are submersed in said chrome bath for two days, whereupon the threads are washed and dried.

All temperatures are indicated in centigrades throughout the specification.

I claim:

1. The method of increasing the strength of artificial fibers made from casein, which com-' prises dry-spinning artificial fibers from an alkaline casein mass, hardening the dry fibers while they are in alkaline condition by treating them strength of artificial threads made from casein which comprises dry-spinning threads from an alkaline casein mass, hardening the dry threads salt to render the solution basic, said solution serving to maintain therthreads stretched, and

then washing and drying the permanently stretched threads.

4. The method of increasing the wet and dry strength of artificial threads made from casein ,which comprises dry-spinning artificial fibers from an alkaline casein mass, hardening the fibers by treatment with gaseous formaldehyde while the fibers are alkaline, freeing said fibers of alkali by treating them with dilute acid, stretching the threads while they are in wet condition to approximately double their length, treatwhile they are still in alkaline condition by treating them with formaldehyde in gaseous form, removing the alkali from the threads by treating them with dilute acid, stretching the threads While they are wet, and while they are still in wet stretched condition treating them with a solu-' tion of chrome alum to maintain them elongated, and then washing and drying the threads.

3. The method of increasing the wet and dry strength of artificial threads made from casein which comprises dry-spinning threads from an alkaline casein mass, hardening the dry threads while they are in alkaline'condition by treating them with gaseous formaldehyde, freeing said threads of alkali by the action of an acid, stretching the wet threads to approximately double their length and while they are in stretched condition passing them through a chromium salt solution containing chrome alum and sufiicient alkaline ing them while in stretched condition with a chromium salt bath at a temperature of approximately 40 C., to substantially maintain the elongation, and then washing and drying the fibers.

5. The method of increasing the wet and dry strength of artificial threads made from casein which comprises dry-spinning artificial fibers from an alkaline casein mass, hardening the fibers by treatment with gaseous formaldehyde while the fibers are alkaline, freeing said fibers of alkali by treating them with dilute acid, stretching the threads while they are in wet'condition to approximately double their length, treating them while in stretched condition with a chromium salt bath at atemperature of approxie mately 40 C., and for a period of at least two days to substantially maintain the elongation, and then washing and drying the elongated fibers.

RUDOLF SIGNEEt. 

